The present invention relates to a method of manufacturing Planar Lightwave Circuits, and more particularly to a method of manufacturing whereby V-grooves etched in a substrate are aligned with a planar waveguide core deposited on the substrate.
It is known that planar waveguide devices fabricated on a silicon substrate may be fibre pigtailed by using integrated V-grooves etched on the substrate. The optic fibre is positioned so as to lie within the V-groove and is thus guided by the groove into alignment with the waveguide core. The V-groove must be precisely aligned laterally and vertically with the waveguide core to allow for effective optical power transfer between the fibre and the core.
Several methods of aligning the V-groove with the waveguide core are known from the prior art. EP 0762 162 discloses a method in which a single lithographic mask forms and laterally aligns both the waveguide core and the V-groove simultaneously during the same manufacturing process. The single mask has laterally aligned waveguide and V-groove portions and is used to pattern a core glass layer to form the waveguide core and to define the location of the V-groove. The V-groove is then formed completely using conventional etching techniques. Unfortunately, due to inaccuracies which occur within the lithographic process it has been found that the technique is unable to provide the desired accuracy for precise alignment of the fibre core with the waveguide core.
A further method is described by Day et al. in Electronics Letters vol. 28 p. 920-22, 1992 in which the V-grooves are etched prior to the deposition of any oxide cladding layers, and then the waveguides are aligned to the V-grooves during the patterning of the core layer. This approach suffers from the drawback that oxide deposition is required on both the front and back of the wafer. This deposition process is an extra processing step which is both time consuming and prone to particle contamination, thus lowering the yield of the devices.